Founder of Zube here. GitHub Projects is going to be very useful for small teams. Also, really excited to see how open source projects will use it. It could add some much needed visibility into their road maps and what they're currently working on.
That said, GitHub Projects is not going to be a great solution for everyone, particularly larger teams. If you're doing serious project management with GitHub you'll greatly benefit from a more full featured tool like the one we make! Zube - https://zube.io